Worst Example...Evar!

gga

Way back in my first year of university, as part of a first year
discrete maths unit we were taught introductory formal logic. After
introducing propositional logic and covering ANDs, ORs and truth
tables, we moved on to implications. For this particular lecture we
had a fill-in lecturer. I can’t remember why.

In explaining implication to us this lecturer used an example that has
stuck with me ever since. This isn’t because it was one of those
glorious examples that are like a light being turned on; suddenly it
is all clear and new vistas of understanding open up. Oh no, this
example was the other kind.

One of those examples that distracts with its own internal errors and
inconsistencies; that steers you in completely the wrong direction;
and, best of all, pollutes your mind enough that you may never
understand the original point.

The bad example:

An implication would be when your mother says to you: ‘If you clean
your room, then you can go to the movies.’ So after you clean your
room, your mother lets you go to the movies and the statement is
true. But if you don’t clean your room and go to the movies anyway,
the statement is also true.

Huh?

Logically, yes, that’s correct. Single implication works like
that. But the world doesn’t, and it’s pretty hard to ignore that
little detail.